Kitchen - Cooker FCU + Grid Switch for Appliances

[Bearman]

I have been an active follower of advice on this site for some time and thought I'd take the jump and sign up. As a newbie, apologies if this question is duplicative, posted in the wrong place or if I've made any other faux pas.

I'm currently learning the trade, but not anywhere near qualified yet. I've got my electrician friend coming to wire up my kitchen in a few weeks, but I said that I'd challenge myself to work out everything and have it laid out to be wired in for when he arrives

Cooker (fully gas) - 4mm TE spur from CU to FCU. Sufficient? If yes, 20amp rating?

(appliance list: fridge, freezer, washing machine, dishwasher, extractor fan)

Appliances (option 1):

Grid switch:

• 2.5mm TE from CU to Grid.
• Use 2.5mm conduit singles to wire grids together
• 2.5mm TE from each grid to a un-switched socket

Would the total drawdown put too much load on 2.5mm from CU to grid?

Appliances (option 2):

FCU Spur:

• Spur FCU's for each appliance from existing 5 sockets
• Unswitched socket from each FCU
• Current sockets on a 2.5mm ring circuit with 32amp MCB on CU

Appreciate any guidance that I can get, I know I am cheating a little on my bet, but I am keen to learn from others.

Thanks,
Bearman

 

[chivers67]

For the Gas cooker You use 2.5mm if just a socket or the ignition/lights. 4mm for one socket is a waste

When you say 2.5 mm feeding the Grid do you mean 2.5mm x2

Personally I'd run a kitchen ring final as I don't particularly like Grid Switches, you don't necessarily need FCUs for each appliance just the extractor with a 3amp?

 

[Bearman]

Good to know, I was only thinking 4mm to future proof for when we move and someone might elect for an electric cooker.

When you say 2.5 mm feeding the Grid do you mean 2.5mm x2

- Sure, wired back in as a circuit and not radial.

Personally I'd run a kitchen ring final as I don't particularly like Grid Switches, you don't necessarily need FCUs for each appliance just the extractor with a 3amp?

- Is it not advisable to at least have isolation for each of the appliances, regardless of whether fused or not? Thanks for the great feedback so far, chivers67.

 

[chivers67]

Ok, run in 4mm if you want to future proof. You could put it in on a 30A MCB. Are your appliances built in? If they are then maybe switched FCU's or the grid method though since the Fridge and Freezer will virtually be permanently on I wouldn't personally put them on a grid. Very easy to switch off accidently at night.

 

[flameport]

Cooker (fully gas) - 4mm TE spur from CU to FCU. Sufficient? If yes, 20amp rating?

Yes, which gives the option to install an electric hob/cooker at a later date.
May as well fit a 32A MCB, the FCU can have a 3A or whatever
for the gas ignition.
Easily changed to an outlet plate if an electric cooker is required in future.

Appliances (option 1):
Grid switch:

A poor choice, and somewhat unnecessary given that the appliances will be switched off somewhere between rarely and never.

2.5mm² on it's own would imply a 20A or perhaps 25A radial, which would probably do for the appliances listed.

If you intended to do a ring with 2x2.5mm² that would be a 32A, but is a poor design as it would be a 'ring' with all the load at one point, and one 4mm² cable would do the same thing - although good luck fitting 4mm² into grid switches.

Another problem is the large number of wires to fit behind the grid switches, and the extra cable used to have everything supplied from a single point.

Appliances (option 2):
FCU Spur:

Could be done, but as with the grid arrangement do you really want racks of switches for appliances which will rarely be switched off?

Is it not advisable to at least have isolation for each of the appliances, regardless of whether fused or not?

Yes, it's called removing the plug from the socket. Something which will be required should any of them need repairs, regardless of any other switches or controls.

 

[Bearman]

Thanks, guys, really useful feedback all combined.

I will plan ahead with a 32 MCB with 4MM TE to FCU for cooker ignition; at least that way, the current set up could support a reasonable electric cooker anywhere up to 7kw at a push.

2.5mm² on it's own would imply a 20A or perhaps 25A radial, which would probably do for the appliances listed.

If you intended to do a ring with 2x2.5mm² that would be a 32A, but is a poor design as it would be a 'ring' with all the load at one point, and one 4mm² cable would do the same thing - although good luck fitting 4mm² into grid switches.

Understood, good point. Current wiring is a 20amp MCB with radial for the kitchen, so it wouldn't be much of a change that way.

Could be done, but as with the grid arrangement do you really want racks of switches for appliances which will rarely be switched off?

Personally, I don't have much of a problem with 5 sockets in the back of cupboard units (at the top), so that isolation is possible easily.

Yes, it's called removing the plug from the socket. Something which will be required should any of them need repairs, regardless of any other switches or controls.

A few electricians in the past have told me that technically, you should be able to isolate an appliance without having to touch said appliance or the CU. Is this best practice or misinterpreting regs? I personally will never turn the appliances off and would happily isolate the kitchen if I needed to remove a faulty appliance, but I just want to make sure that what I do wouldn't be questionable; I'd happily have a single socket behind each appliance.

Are your appliances built in?

The dishwasher, fridge and freezer will be integrated appliances. Cooker and washing machine are free standing

 

[flameport]

you should be able to isolate an appliance without having to touch said appliance or the CU.

There is no regulation which requires that, and in any event the circuit can be switched off at the consumer unit if appliances need to be removed.

Socket behind each one is an option - just be careful with integrated appliances, as they often have very little space behind them.
A socket in the adjacent cupboard is another possibility, so that appliances can be unplugged before moving them - and that can be done whether they are integrated appliances or free standing.

It's certainly possible to have FCUs or grid switches, plenty of kitchens have such things. Some people seem to want them.
However it's not necessary, and it just adds extra cost and more things to go wrong.

 

[Bearman]

It's certainly possible to have FCUs or grid switches, plenty of kitchens have such things. Some people seem to want them.
However it's not necessary, and it just adds extra cost and more things to go wrong.

Really appreciate the detailed explanation, makes plenty of sense. Placing in the adjacent cupboards sound like a good should for the integrated appliances. Last question, all of what I've described, apart from the cooker, is fine to run as ring final on the 32MCB?

 

[sparkwright]

Why is it a major problem for a ring to have most of the load in one area?

What difference will it make? All the switches will be on the ring, with an individual cable to each appliance. The ring feeds from both ways.

There's no rule about how short the cables between accessories can be.

I would think most kitchens have this problem.

 

[flameport]

is fine to run as ring final on the 32MCB?

Yes, provided it's installed as a proper ring and all of the tests applicable to a ring are done in the correct way.

 

[flameport]

Why is it a major problem for a ring to have most of the load in one area?

If the load is at or near the centre of the ring, then no problem, but such an arrangement would be better served with a 4mm radial.

If the load is not at the centre, the current in each leg will not be the same, and there is a possibility of overloading one leg.

 

[sparkwright]

If the load is at or near the centre of the ring, then no problem, but such an arrangement would be better served with a 4mm radial.

If the load is not at the centre, the current in each leg will not be the same, and there is a possibility of overloading one leg.

Ok, thanks.
Maybe, if you've got a bit of spare cable, this would make a good demonstration in your series of YouTube videos, which often show similar ideas.

 

[jg321]

Maybe, if you've got a bit of spare cable, this would make a good demonstration in your series of YouTube videos, which often show similar ideas.

Agreed. Ideally with flames.

 

[JohnW2]

Why is it a major problem for a ring to have most of the load in one area?

If the load is at or near the centre of the ring, then no problem, but such an arrangement would be better served with a 4mm radial. .... If the load is not at the centre, the current in each leg will not be the same, and there is a possibility of overloading one leg.

One thing to bear in mind is that if, as commonly the case, a circuit is wired with Method C 2.5mm² cable, then one "hardly needs" a ring circuit - a 27A radial (if one could find a 27A MCB!) would be compliant and, with a ring, the CCC of the cable (27A) is so close to the In of the OPD (32A), that an entire 32A load 'at one point' would have to be within about 15% (of the length of the ring) from one end of the ring for the 'short leg' of the cable to be overloaded.

If (as I suspect will very commonly be the case), the total load on the circuit never exceeds 27A, no part of the circuit can ever be overloaded, no matter how close the loads to an end of the ring.

In fact, the regulations only require that no part of the cable "is likely to be overloaded for long periods" and I do doubt that, even in kitchens, the total load is "likely to exceed 27A for long periods". If one believes that (and if it is Method C 2.5mm²), then it does not matter how close the loads are to an end of the ring.

Kind Regards, John

 

[scousespark]

Why not let you mate design this for you and explain his decisions. He is on site so can better decide than anybody here.